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indexingjulialogical-operators

combining logical operations in indexing array - Julia

Given a 1D array in Julia, find all elements which are between a (= 4) and b( = 7), in place.

a = 4;b = 7;
x = collect(1:10)
x[isless.(x,a)]

will find all the elements in array which are less than a = 4.

How to combine two logical operations in indexing.

 x[isless.(x,a) && !isless.(x,b)]

is not working out.

Solution

  • If you are OK with < operator instead of isless (which is most likely the case unless you work with NaN, missing, or -0.0) then you can write:

    julia> x[a .< x .< b]
2-element Vector{Int64}:
 5
 6

    Alternatively you can use filter:

    julia> filter(v -> a < v < b, x)
2-element Vector{Int64}:
 5
 6

    which brings me to the reason why I added this comment. You asked for an in place operation. This is not possible with indexing, but you can achieve it with filter! if you work with Vector:

    julia> filter!(v -> a < v < b, x)
2-element Vector{Int64}:
 5
 6

julia> x
2-element Vector{Int64}:
 5
 6